po420

I have the po420 code on my van. It is a 96 astro 2wd, 4.3 vortec. Also has a little bit of a miss when going up an incline on the highway with the cruise on, under light throttle. Doesn't do it at idle or if u power brake it. I was having some cold start problems and just replaced the fuel pump, filter, and pulsator, that fixed the cold start problem cleared the code and it came back. Any ideas? replaced the plugs, wires, cap and rotor about 30k ago. The heater will burn u out, but the temp guage hardly gets over 150 replaced the thermostat about 1k ago. I need lots of help here guys lol. Thanks in advance

I just searched the trouble code list for OBD II in my manual and couldn't find a PO420 code. So I'm stumped. Anyone else?

P0420: "Catalyst efficiency below threshold (bank 1)

Probable cause: Oxygen sensor on bank one. Worst case: Bad catalyst on bank one.

P0420: "Catalyst efficiency below threshold (bank 1)

Probable cause: Oxygen sensor on bank one. Worst case: Bad catalyst on bank one.
so would that be the one on the drivers side that is bad or the one after the cat because they are both considered bank one. I have replaced the one before the cat about 30k ago. thanks

P0420 is monitoring catalyst "performance" or "efficiency" by comparing upstream and downstream oxygen sensor voltages within a given parameter. This DTC would be indicating the downstream, (after the catalyst) sensor, or catalyst itself.